LUMINESCENT HOMOATOMIC EXCIPLEXES IN DICYANOARGENTATE(I) IONS DOPED IN ALKALI-HALIDE CRYSTALS - 1 - EXCIPLEX TUNING BY SITE-SELECTIVE EXCITATION

The photoluminescence behavior of dicyanoargentate(I) ions doped in KC I host crystals has been studied. Several ultraviolet and visible emis sion bands are observed in this system. Each emission band becomes dom inant at a characteristic excitation wavelength; that is, the energy o f the emission can be tuned by site-selective spectroscopy. Both the e xperimental and the theoretical results suggest the formation of Ag-Ag -bonded excimers and exciplexes between adjacent Ag(CN)(2)(-) ions in the host lattice. The experimental evidence includes the broadness, th e absence of detailed structure, the large Stokes shifts, and the very low band energies of the luminescence bands. Meanwhile, ab initio cal culations show that the LUMO is bonding with respect to Ag-Ag bonds wh ile the HOMO is antibonding. Moreover, excited state extended Huckel c alculations indicate the formation of exciplexes with shorter Ag-Ag di stances, higher binding energies, and higher Ag-Ag overlap populations than the corresponding ground-state oligomers. The emission bands are assigned to different [Ag(CN)(2)(-)], luminescent exciplexes. Tuning of the emission over the 285-610-nm range has been achieved by site-s elective excitation in a single KCl:Ag(CN)(2)(-) crystal. The results in this work give rise to a new optical phenomenon we call ''exciplex tuning''.